Electronically controlled light-beam diverters, so-called deflectors, are employed for example in the case of optical memories or laser TV displays and the like. An important property of such a deflector is the achievable number of resolvable points, i.e. of individual angularly separated light-beam positions which can be generated. Known is the construction of a deflector with the aid of a prism, whose refractive index can be changed electro-optically. With a single prism of this type it is however possible to generate only about from 10 to 20 resolvable points. This is inadequate for most applications. For example, approximately 1,000 resolvable points are needed for application in a laser TV display. The option of arranging several prisms one behind the other, to increase the number of resolvable points, entails the disadvantage that the length of such a composite deflector would be correspondingly large. Light deflectors with a line of prisms arranged side by side do not have this disadvantage. In that case, each prism deflects a part of the light-beam, and to be sure in such a way that the entire beam is oriented in the desired direction once it has passed the deflector. To prevent destructive interference of the partially deflected partial beams in the remote radiation field, means are also known which permit the phase of each partial beam to be controlled electro-optically. Used for this purpose are a number of control electrodes, which are respectively positioned in front of the prism electrodes, arranged in the shape of a wedge, which form the prismatic deflection fields (DE 3,025,096 A1).
Electro-optical light-beam deflectors with deflector prisms arranged side by side, i.e. in the shape of a prism array, have been constructed both with so-called volume prisms (Yuichi Ninomiya, Ultrahigh resolving electro-optic prism array light deflectors. IEEE Journal of Quantum Electronics, QE-9, No. 8, August, 1973, pp. 791-795) as well as with integrated-optics waveguide prisms (DE-3,025,096 A1). The main problem with prism-array deflectors is the generation of an ideal sawtooth curve development of the refractive index changes without roundings at the prism necks and without distortions between the prisms, from each deviation from an ideal curve development leads to amplified sidebands and worsening of the signal-noise ratio.
With volume prisms it is practically impossible to produce an ideal sawtooth curve development. Aside from the fact that it is technologically very inefficient to assemble such a deflector from individual crystal chips in order to achieve sharp boundaries between at least a few of the prisms, the thickness of the chips through which the light-beam passes is relatively large due to technological requirements and amounts to at least 200 .mu.m. The result of this is that the electrical field distribution in such a chip is very inhomogeneous. As a consequence, the refractive-index plot exhibits large deviations from the ideal curve. These deviations are greatest in the center of the chip, the deviations being smaller, on the other hand, near the electrodes. A further disadvantage caused by the thickness of the chip is the high control voltage that must be used, approximately 1 kV, if an acceptable number of resolvable points is to be achieved.
The solution with waveguide prisms has the advantage over that with volume prisms that the light is guided in a thin layer, permitting a reduction in the magnitude of the control voltage applied to the electrodes. Due to the unfavorable electrode geometry, this must still be about from 400 to 500 V. Even this solution does not present the possibility of producing an ideal saw-toothed distribution of the refractive-index change. The reason for this is the extremely inhomogeneous electrical-field distribution between the electrodes mounted on the surface of the waveguide, which in turn produces distortions in the deflected light beam. The unfavorable electrode shape likewise restricts dimensions of the prism. To permit the use of a control voltage which is not excessively large, prisms are designed with a width of only about 50 .mu.m. An aperture of 1 cm is necessary, if 1,000 resolvable points are to be achieved, i.e. about 200 prisms and an equal number of control voltages are needed, which brings with it the disadvantage of the comparatively great complexity of the control electronics required to achieve this.
The problem addressed by the invention is therefore to create a planar electro-optical light-beam deflector of the initially cited type, in which the disadvantages listed above are avoided and which exhibits a nearly ideal saw-toothed curve development. The invention addresses the problem, in addition to that, of creating the most efficient possible process for the production of such a light-beam deflector.